1. FIELD OF THE ART
The present invention relates to a method for sealing a plastics lid to a container of plastics-coated paper board, the lid preferably being put down over the top edges of the container with a certain holding pressure for closing of the container, and the lid preferably being provided with a substantially U-shaped groove extending along the circumference thereof and being open in the downward direction, said groove serving to receive the top edges of the container.
The invention also relates to an apparatus for carrying out the method.
2. DESCRIPTION OF THE PRIOR ART
A known method for sealing a lid to the top of a container consists in supplying heat to the lid and thereby to the container by heated jaws which are pressed against the lid. In such a method heat is supplied to the lid and the container by heat transfer from the outwardly facing surfaces and into the lid and the container. Consequently, the temperature at the outer surfaces must be higher than the temperature within the material to be heated, and a rapid heating requires a very high temperature of the jaws.
Such a heat supply by heat convection through heated jaws is not very convenient for sealing a plastics lid to a container of plastics-coated paper board in running production, because the supply of the necessary energy will require too much time unless the temperature of the jaws is kept very high. However, such a high jaw temperature implies that a plastics lid which has been manufactured by vacuum moulding will deform and shrink.